1. Field of the Invention
The present invention relates generally to the measurement of ultraviolet radiation, such as produced by the sun. More particularly, the present invention relates to collecting, processing and displaying information relating to ultraviolet radiation so that it can be used to warn the public of potential health hazards that may arise from ultraviolet radiation exposure to the sun.
2. Description of the Prior Art
It is desirable to know the relative level of ultraviolet radiation from the sun when engaged in outdoor activities. The damaging effects of exposure to certain ultraviolet wavelengths, in the spectral range of 290 to 320 nanometers, have been recognized for a long time, and a number of methods and devices have been developed to determine a safe exposure. These devices include ultraviolet radiometers, sunburn meters, ultraviolet dosimeters and the like. These devices do not, however, give a wide segment of the public virtually instantaneous warning of the dangers of ultraviolet radiation. No known device displays ultraviolet radiation levels to the public, whether or not those levels are known dangerous wavelengths. Further research may find dangers, or at least the desirability of skin protection, in the broader bandwidth of 290 to 400 nanometers in the ultraviolet range.
Current devices for measurement in the known dangerous range are typically individualized and require elaborate measurement or interpretation, requiring engineering or other technical knowledge to use. In most of the recreational areas where the public is exposed to sunlight, such as ski resorts, beaches or on the deck of a cruise ship, there is little time for objective assessment of the risks of overexposure to ultraviolet radiation. Very often, the danger of sunburn is mistakenly associated with the intensity of the visible light emanating from the sun, and it is well known that the ultraviolet radiation when a sky is covered by haze can be as dangerous as direct sunlight. In addition, the increase in the intensity of ultraviolet rays with altitude does not follow any apparent increase in the visible sunlight. A false impression of safety can be given to the public due to the fact that biological warnings, such as irritation and burning, are often delayed and only occur several hours after exposure.
The dangerous rays, in the spectral range of 290 to 320 nanometers, are transmitted or reflected differently from visible light. The dangerous rays are, therefore, unpredictable, and only devices sensitive to the particular spectral range can provide the necessary information. Examples of such devices include photo detectors sensitive to the particular range of spectrum and which provide a signal proportional to the intensity of the rays received. Devices of this type are described in U.S. Pat. No. 3,710,115, issued to Jubb, and in U.S. Pat. No. 3,742,240, issued to Jonasson. The described devices are provided with integrating circuits to relate the measurement to a maximum dose of exposure. Photochemical detectors showing a gradual color change in a self-integrating device can be calibrated to have optical densities of coloration corresponding to a given dose of radiation Examples of such devices are described by Zweig in British Patent No. 1,507,486; Frankenburger in U.S. Pat. No. 1,845,835; Graham in British Patent No. 1,422,631; Dickinson in British Patent No. 1,573,407; and Robl in German Patent No. 489,671. All of these devices are sensitive to irradiation on the surface of the skin.
Still another photochemical detector provides direct information relative to the reaction of the skin to ultraviolet radiation by measuring the radiation reflected by the skin, as described by J. Robillard in U.S. Pat. No. 4,705,046.
Photo detectors sensitive to the spectral range of 290 to 320 nanometers, described above, measure watts per square centimeter or per square inch and are mostly directed to scientific or atmospheric data collection. Photochemical devices, also as previously described, provide an evaluation only of the dose of the radiation. Such photochemical devices require visual comparison of color densities and, as a result, at least a minimum of attention to the ongoing process. This is a drawback rendering such photochemical devices unsatisfactory for use by the general public. Consequently, there is a need for a quick warning system informing the public of the intensity of ultraviolet radiation and its evolution over a fixed short time period.